The present invention is directed to a method of streak detection in papermaking and more specifically to a method which is automatically done by computer techniques.
Computer control systems are well known for monitoring the characteristics of a moving sheet of paper, such characteristics including moisture, basis weight, and caliper, and using this monitored information to control what are known as actuators, to control the parameter to a desired set point. Even with such control, anomalies in the machine direction, that is the direction of the moving sheet or web, may occur. These are known as streaks and such streaks can and are seen on a visual display unit which has been color coded in conjunction with present day computer control systems. Such a display may be used by an operator to tune or correct an actuator. After the operator views several of the streaks, however, the control action is very subjective. In addition, the true magnitude of a streak is obscured by noise and there may be many minor anomalies of no consequence thus obscuring the overall control picture.
It is therefore a general object of the present invention to provide for an automatic method of detecting streaks.
In accordance with the above object, there is provided a method of detecting streaks, anomalies of a parameter of a web in a machine direction, in a machine producing a moving web which moves in a machine direction, having a plurality of actuators in a cross-direction to the machine direction for controlling a predetermined parameter and having a scanner moving across said web of sheet material in a cross-direction, the scanner measuring in a cross or profile direction a predetermined parameter of the web, to thereby detect data relating to said streaks, with a plurality of data boxes, each data box containing data as to a parameter at an instant of time for each of a plurality of said profiles. The method comprising the following steps of computing the moving average of the data detected in x number of profiles, for example, 10 profiles, and determining an average of the data box data.
A height, H, is chosen which is a number related to the value of the predetermined parameter, which is dependent on the quality and use of the web which is the maximum allowed deviation from the average.
Residuals, Ri, are computed from the average and checking for the absolute values of Ri greater than H by counting consecutive data boxes with a parameter value greater than H, where i is 1xe2x88x92N, where N is equal to the number of data boxes in a profile.
A value, W, is chosen depending on quality and use of the web, which is a number equal to the consecutive number of data boxes to define a streak.
If the count of consecutive data boxes is equal or greater than W, the profile location of the streak is stored, namely its location along the machine direction and along the profile of the web for use in correction of the actuator to minimize such streak.